1. Field of the Invention
The present invention relates to a multi-type air-conditioning system with a fast hot starting for a heating operation and, more particularly, to an air-conditioning system with a fast hot starting for a heating operation, which is constituted by heat pump type refrigeration cycles including an outdoor unit having at least one variable-capacity compressor, and a plurality of indoor units.
2. Description of the Related Art
In a multi-type air-conditioning system of the above-mentioned type, one or two variable-capacity compressors in an outdoor unit are driven at a predetermined operating frequency in accordance with a required capacity of each indoor unit. With this operation, a required amount of a refrigerant is supplied from the outdoor unit to each indoor unit through a refrigerant flow control valve, and desired air conditioning in each room is attained.
FIG. 9 shows a conventional multi-type air-conditioning system of this type.
Reference symbol A denotes an outdoor unit including one or two variable-capacity compressors. A branch unit B is connected to the outdoor unit A. A plurality of indoor units C1, C2, and C3 are connected to the branch unit B through a plurality of refrigerant flow control valves incorporated in the branch unit B.
More specifically, the indoor units C1, C2, and C3 respectively send required capacities corresponding to the respective air-conditioning loads to the branch unit B as frequency setting signals f1, f2, and f3.
The branch unit B obtains the required capacities of the respective indoor units from the frequency setting signals f1, f2, and f3, and sends a frequency setting signal f0 corresponding to the sum of the required capacities to the outdoor unit A.
The outdoor unit A controls the operating frequencies of the compressors in accordance with the frequency setting signal f0, and supplies a refrigerant from the compressors, as a required amount of a refrigerant, to the respective indoor units C1, C2, and C3 through the refrigerant flow control valves in the branch unit B.
Assume that a heating operation is started by using an indoor unit having the minimum capacity of such a conventional multi-type air-conditioning system in a very cold room early in the morning in a winter season in which heating operations are required. In such a case, since the capacity of the indoor unit is smaller than that of the outdoor unit, the operating frequency of the compressor cannot be sufficiently increased by only a required capacity command from the indoor unit. Therefore, it is difficult to sufficiently heat piping normally having a length of 10 meters or more or an indoor heat exchanger within a short period of time.
In addition, the indoor unit includes a function for preventing cool air from being blown by inhibiting an air blowing operation until the temperature of the indoor heat exchanger reaches a predetermined value. For this reason, warm air is not blown (hot starting is not performed) into the room for a considerably long period of time, i.e., hot starting in a heating operation is very slow.
Such an inconvenience occurs when a heating operation is resumed upon a defrosting operation as well as when a heating operations is started.